1. Field of the Invention
The present invention relates to a video projection system, and more particularly, to a method and apparatus for increasing visual contrasts of the video projection system, such as a video projector, as it is operating in brighter ambient light, such as daylight and room light, environments. Further, the present invention provides a reflection screen with a reflection screen surface only enabling color spectrums of primary colors of red, green, and blue to be reflected, and the present invention reflection screen further incorporates with an illumination lamp emitting the light having spectrums just locate on gaps between blue-green and green-red color spectrums, for the use of room illumination.
2. Description of the Related Art
There are many applications that need a screen to have projection images displayed thereon, for the slide show, presentation, or movies, through devices such as overhead projectors, slide projectors, movie projectors, and video projectors. One of the most popular projection systems is the movie projector that projects the film images to the large screen, so that many people can watch these images from the large screen at the same time. For the purpose of having a better image projection effect on a large screen, images used in movie theaters inherently have wide ranges of light intensities and evenly require an environment having a comparatively dark light projected on the projection screen. As for slide projectors or overhead projectors, even they are for still pictures of texts or graphics projection in a normal room light environment, the light outputs from these sorts of projectors have to be much greater than that of the ambient environment.
Video projectors are also available to function as well as movie projectors. In this case, video projectors incorporate with controlled environment lights so as to simulate a home theater. Video projectors also can display still images such as texts or graphics in any given environment with the room light for presentation purpose, as long as the intensities of lights outputted from the projectors are much greater than the light intensity of the environment.
A projection system with a strong light source for image projection through optical lens and focusing the images on the reflecting target such as a screen is necessary when it comes to the image or picture display. The screen is designed to reflect lights covering full light spectrums to: viewers. As some other ambient environment light sources exist, lights such as the sunlight or the room light from any given lamps outputted from these ambient environment light sources are also reflected by the screen to viewers. Due to the screen reflects all environment lights to viewers, environment lights therefore affect the dark image levels of images projected on the screen and then reflected back to viewers. For example, if an image contains light intensity levels ranging from 1 to 100, wherein the light intensity level of 1 represents the darkest image level and that of 100 is indicative of the brightest image level in this image, and if the screen is with 70% efficiency in reflection, the darkest and brightest (light intensity) levels of the reflected images turn into 0.7 and 70, respectively. In this case, if the environment light reflected from the screen is with the intensity level of 10, reflected images with light intensity level less than 10 are comparatively very difficult to be viewed, meaning only images with intensity levels ranging from 10 to 70 will be recognized with ease. Therefore, that""s why all environment lights in movie theaters should be turned off or shed, in order not to affect the images supposed to be viewed.
Video projectors, which have increasingly become more and more popular, mostly operate in the bright environment such as the meeting room or classroom with the daylight, having to output lights with greater light intensities as compared with those in the bright environment. For example, if the environment is with the brightness of 50 lumens, and, for the purpose of superior projection performance from the standpoint of viewers, a contrast ratio of 100:1 is required, representing video projectors have to be capable of outputting 5,000 lumens. As the environment is with the brightness of 20 lumens only, projectors require2,000 lumens output capability to have the same contrast ratio, but, however, such environment is not suitable for reading. Thus, there is an emerging demand for screens of having the reflected environment light reduced and the light contrast ratio increased simultaneously. For example, a screen is capable of reflecting 80% of the video projector light but 20% of the environment light, and thus, with this screen, to have a 100:1 contrast ratio under the environment light of 50-lumen brightness, projectors with 1,250 lumens are required. While in comparison with traditional video projectors with the 5000-lumen output, those projectors with 1250-lumen outputs not only can have the same image-viewing effect but also pose less harm to human eyes.
Referring to FIG. 1 shows a projection screen 100 with surface reflection material 120. When a projection image light 121 through the lens is projected on the screen, the reflected lights 123 of the projected light 121 are shown to illustrate the effect of reflection. FIG. 2 is a side view of FIG. 1, and FIG. 3 is another side view of FIG. 1 while taking the ambient light 130 into consideration. As same with the projected light 121, the ambient light 130 as well will be reflected upon being projected on the reflection surface 120. Light intensities of the reflection for the projected image light 121 and the ambient light, both of which rely on the characteristic of the reflection surface 120, are not significantly critical to the present invention. The ambient light 130 also has its own corresponding reflections, such as the reflected light 135. However, please refer to FIG. 4, FIG. 4 assumes that the input light 200 is with the light intensity (Y-axis) ranging from the darkest (bottom) to the brightest (peak) in terms of the intensity amplitude of 202. While the reflected ambient light 201 is taken into consideration with the reflected projected light 200, the amplitude 202 of the reflected projected light 200 will be lowered to the amplitude of 203, due to the presence of the reflected ambient light whose light intensity is uniformly with the amplitude of 201. As the reflected ambient light 201 covers the darker lights of the reflected projected light 200, the contrast ratio eventually will be reduced because the current reflected projected light 200 is only with the light intensity having the amplitude of 203. In other words, the gap between the darkest to the brightest portion of the current reflected projected light 200 is with the amplitude of 203, and, as compared with the amplitude of 202, in the case of having no ambient light taken into consideration, the amplitude of 203 is smaller than that of 200, representing the contrast ratio has been lowered down.
The present invention has been made in consideration of the above-described weakness shown in traditional arts and is particularly applicable to a front projection screen for a video projection system through having predetermined color reflectors placed thereon. Thereby, these color reflectors serve as color filters, to have images with colors within spectrums of these color reflectors reflected, but colors beyond these predetermined spectrums not reflected. Traditionally, a front projection screen for a video projection system still reflects the ambient environment light with images projected from the video projection system together, leading to the reflecting factor of the ambient light from different angles will not be reduced. Even with the use of curvature screen or having glass beads placed on the screen, for enhancing the screen gain, the viewable angle will be narrowed down accordingly. With the present invention, the screen, which has evenly distributed primary color cells placed thereon, will only reflect images with color spectrums within spectrum ranges of these three primary colors (red, green, and blue) and absorb other color spectrums outside aforementioned spectrum ranges. These color reflecting cells are chosen as R (Red), G (Green) and B (Blue), so as to reflect most light spectrums outputted from the video projector of the video projection system and absorb other lights including the room light and daylights, thereby, bringing up a projection screen with an increased contrast ratio.
According to one aspect of the present invention, R, G and B reflecting cells are evenly distributed and coated on the surface of the screen. Most video projectors employ three primary color (RGB) light sources to generate corresponding images, as most of the ambient light, such as the daylight and room light, consists of a continuing full color spectrum. The present invention screen only reflects images with spectrums of three primary colors and absorbs other color spectrums, therefore, reducing the reflection of ambient lights from the screen.
Reflecting cells with three primary colors are with spectrums of 660 nm (Red), 525 nm (Green) and 430 nm (Blue) and are printed or chemically coated on the screen surface. Still, grinded red, green and blue glass beads may serve as corresponding reflecting cells as well. Portions of the screen not covered by these reflecting cells are designed to be black, so as to absorb other light spectrums. Additionally, color fibers that thread to corresponding RGB textiles and are laminated on the reflection screen provide an alternative to the choice of reflecting cells.
According to another embodiment of the present invention, the illumination lights for the presentation room with the present invention projection screen can take advantage of intersections of blue-green and green-red spectrums through the fluorescent phosphor compound to generate spectrums such as of 480 and 590 nm. Therefore, with such illumination lights, the minimum power of the illumination light will be reflected from the screen only having spectrum reflections of red, green and blue happen.
Accordingly, an important object of the present invention is to provide generic solutions for a projection screen with an enhanced video projector""s light reflection and a reduced ambient light reflection.
Other objects, together with the foregoing are attained in the exercise of the invention in the following description and resulting in the accompanying drawings.